Metallurgy of tin



Patented Nov. 23, 1922.

UNITED sures WOOLSEY KuA. JOHNSON, OF HARTFORD, CONNECTICUT.

METALLUBGY OF TIN.

11o Drawing.

To all whom it may concern:

Be it known that I, Woonsnr MoA. J onu- SON, a citizen of the UnitedStates, residing at Hartford, in the county of Hartford,

State of Connecticut, have invented certain new and useful Improvementsin Metallurgy of Tin; and I do hereby declare the following to be afull, clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

This invention relates to the reduc ng and refining of refractory ores,particularly those containing two or more elements wh c are separatedwith difliculty, the invention being particularly adaptable to thetreatment of ores of tin, containing iron.

It is the object of my 1nvent1on to provide a method of reducing andrefining ores,

wherein a sharp and well defined separation of the elements is possible,thus simplifying the operations required to recover the metal,increasing the efliciency of the reduction, and lowering the cost ofoperation thereof.

Another object of the invention is the provision of a simple andeilicient method of recovering tin from its ores, particularly such -ascontain more or less iron and other elements including so-called complexores containing sulfur, antimony, arsenic, bismuth, lead, silver andgold, as well as iron.

Further objects and advantagfs of my invention will be apparent as it isetter understood by reference to the following specification containinga detailed statement of the best mode of a plying my invention inspecific cases, it ing understood that the method will necessarily bevaried in accordance with the peculiar characteristics of the oretreated.

In the following specification I shall describe the application of myinvention particularly to ores of tin, by way of illustration and inorder that a clear understanding of the method and its attendantadvantages may be acquired. It is to be appreciated, however, that theprinciples which underlie the method are of general application to oresof similar character, and that the method may be advantageously employedin the reduction and recovery of other metals than tin from their ores.

Ores of tin generally carry more or less iron, some of which issusceptible to mechanical separation. A certain amount of Applicationfiled Kay 20, 1919. Serial No. 298,413.

iron invariably remains in the ore and its removal from the tin afterreduction thereof 15 attended by numerous disadvantages, in thesuccession and variety of expedients which must be adopted, and in themore or less troublesome products which result from the variousoperations. In the smelting of tm ores as conventionally practiced inreverberatory or shaft furnaces, no sharp and clear cut separation ofthe tin from the iron 1s possible. The products of such an operation arecrude tin containing iron and a slag high 1n tin oxide. The tin must belaboriously and expensively refined before it becomes a commercialproduct and the slag must be retreated to recover the tin therefrom.

I have discovered that a well defined separation of the tin and iron, inores containing these metals, may be accomplished through theapplication of my invention as hereinafter described. In applying mymethod, the ore is subjected to a preliminary reduction in the presenceof a reducing gas, such as hydrogen or carbon monoxide, under conditionscarefully controlled and regulated to permit a selective or differentialreduction of the tin oxide, leaving the iron oxide substantiallyunafi'ected, and favoring the reoxidation of any iron which may bereduced during the operation. The regulation contemplated involves thewithdrawal of the gaseous end-products steam, carbon dioxide or mixturesthereof for example, depending upon the nature of the reducing gasemployed, at such a rate as to permit reduction of the tin oxide withthe greatest rapidity, while insuring the reoxidation of any reducednascent iron. At the completion of the reaction all of the iron presentis in the oxidized condition while substantially all of the tin ispresent in a metallic form. Such regulation is possible because thereaction is reversible and, therefore, strongly influenced in accordancewith the law of mass action b the proportion of endproducts which remainin contact with the material treated. Following the preliminaryreduction, the ore is removed without contact with the atmosphere to asuitable furnace where it is smelted in contact with a slag whichscorifies the iron present in the mass and leaves the tin in asubstantially pure condition.

In carrying out the invention, the preliminary reduction is preferablyconducted in a contemplated of preheating and pre-reducsuitable retortor muflle, either of the vertical in the ore, is many times see thanwhen a or inclined-rotary type, wherein the ore is cofil, non-reducedmixture is charged to the sub'ected at a temperature which ispreffurnace for a far greater smelting rate is eral ily in theneighborhood of 600 to 750 attained. (1., to the reducing influence ofhydrogen, As a specific application of my invention, carbon monoxide orother reducing gas, or I shall describe the treatment of a typicalmixture thereof, until the tin oxide has been ore of complex typecontaining Sn 69.0%, completely reduced. Preferably, the gas is SiO3.5%, Al,O, 2.0%, FeO 5.5%, together 10 applied to the ore on thecounter current with traces of As, Sb Bi, S, Zn, Pb, Au and principle,the fresh gas encountering the re- Such an ore is representative of thedueed ore. The end-products, which, in the olivian tin concentrateswhich have hereevent that hydrogen is employed as the retofore beencommercially undesirable beducing gas, will consist of a mixture ofcause of the difliculty experienced in sepa- 15 hydrogen and watervapor, are removed rating the tin content from the impurities dur' thecourse of the reaction, the rementioned. While available in considerablemov bein re lated so that none of the quantity, such ores have not beenworked to below the ferrous oxide, any extent. Some ore of this type hasbeen while the stannic oxide is reduced at a maxiconcentrated by 'wetmethods when sufii- 2 mum rate. The uncombined hydrogen is ciently rich,but such utilization has been preferably recovered for I a-I189 bypassing limited, the ores being sold at a discount bethe gas overcalcium chloride, anhydrous cause of the expense involved in recoveringsulfuric acid or other hydnoscopic material, the tin. whereby the wateris removed or by refrig- I have discovered that it is possible to 25eration and com ressing. If carbon monseparate the impurities in aninexpensive oxide is employe as the reducinaagent, the and efiicientmanner by heating the ore with end-products will contain car 11monoxchlorine at from 250 to 350 C. The tin, ide and carbon dioxide. Thecarbon dioxide being present as oxide, $110,, is not afl'ectedmay beremoved by absorption in calcium by the chlorine, whereas arsenic,antimony,

30 oxide and the carbon monoxide may then bismuth, and such of the tinas is present in be re-used. A mixture of hydrogen and carthe form ofsulfide, are converted into the hon monoxide may be advantageouslyemrespective chlorides which may be fracployed, as a reducing agent, inwhich event tionally separated by heating. Lead, zinc, the water andcarbon dioxide are separated iron, silver and gold, when present, aresimi- 35 from the end-products by dehydration in larly converted intochlorides and chlorides the manner described and by contact with ofzinc, lead, gold and iron are removed by calcium oxide. Mixtures ofhydrogen and leaching with acidulated water-and chloride carbon monoxidemay be readily produced of silver is separated b leaching with a byelectrolysis of water, providing hydrogen solution of Na,S,O or CN. Thusa tin 0 and oxygen, and the com ination of the oxyore carrying smallamounts of Fe,,O,,, Si(), gen with carbon in a suitable gas producer.and silicates is obtained which is comparable The ore, following thepreliminary reducwith Cornish tin ore. This ore is mixed tion, ispreferably treated in an electric for with substantiall 18.3% by weightof slag nace of the slag-resistance type. This type and 2.5% of C'a(93.6% pure). The slag 5 of electric furnace is not well adapted foremployed is one of the products of the rocreduction of ores because thechemical heat ess, about 600 pounds being produce for required. forreduction is far greater than every ton of ore smelted. The slag analzes the sensible heat of melting and, when a Fe() 20%, CaQ 20%, S110 19%and i0 strongly endothermic reduction mustbe per- 30%, undetermined 11%.The mixture is 50 formed, as in the present instance, the abheated, in avertical or inclined revolvin sorptlon of heat proceeds with suchrapidity muflle or retort, externally fired, to a maxithat the slag ischilled, unless great care be mum temperature of about 750 C. and aused, and the flow of heat through the reducing analyzing, for example,93% chilled slag from the sources of generation H, 2% O and 5% CO and COis con- 55 tothe points of utilization is slow and irducted through theretort in contact with regular. The slag-resistance furnace is, thecharge. The operation of preliminarily however, well adapted to theaccomplishreducing the ore may be conducted continument of my presentpurpose. The ore is ously or intermittently. If the character of reducedprior to delivery to the furnace and the ore is web as to make controlof the 60 is preheated. It does not chill the slag. reaction diflicult,intermittent operation is Moreover, no heat is absorbed in reducingrecommended. the ore in the resistance furnace so that the Where arevolving muflle is employed, the slag remains fluid and serves as anadmirable tin, after reduction forms a mass of small vehicle for heat.Consequently, the conmolten pellets separated by the non-fusible 65sumption of power, under the conditions portion of the charge whichamounts genresult that the 'oftinores,as

the surface of the tin oxide particles by am e,

in the erally by volume to 90% of'the' metal. Where a revol muflle isused, a lower temperature than 50 C. suflicee tor the accomplishment ofthe desired result inasmuch as the reduced metal is removed fromparticles of molten metal, which, through the agitation of the contactsucces' sively with the particles 0 unreduced material. The lowertemperature favors the product because any iron reduced is not soreadily by the tin and is permi to re-oxidizo in contact with theend-produc which are withdrawn at a carefully regulated rate, calculatedto insure the desired insults. The reaction may also be assisted b theintroduction-of small amounts of air-whrch' instantaneously oxidizenascent, and thereforapyrophoric men, while the tin is comparativeyunaffected.- The reduced material is then removed, either directly, orthro h the intermediary of a-hermetically seale ore car, into a slagresistance electric furnace. Here the masses heated to a temperature. ofsubstantially 1200 C. with the iron is scorified providing a abovereferred to, analyzlng. for ex- FeO 20%, Geo 20%, SnO 19% and Si 30%.The tin is separated and carries substantially 1% of-iron. The crude tin1s heatedin contact with the slag, either in the same or another furnacepermittingthe IIOIlslag 'to react with an stannous oxide preach toproduce tin an ferrous oxide and a refined more than 25% impuritiesslagIn the event that an extremely'purc tin is cin atmosphere, for exam is,hydro? n,- ari d is refined electrolytilaally in a Thum box-anodeemplujyi'ng a porous diap and active circ trol A product which is 99.95%pure tin 1s thus produced.

The foregoinug description should enable any person ski d in the art to.practice the intention in its apfilication to. the reduction we as tothe treatment of other ores of similar characteristics. For exampl oresor iron and ma anese ore containing iron, cop r and nick e may besimilarly smelted or the oxides otthe more reguired, the pro-reduced oreis cooled in a re u diflicultly reducible metals such as aluminum mm andmanganese I preferably employ a metallic vapor such as zinc at atemperature of from1700 to 1800 C. as' the reducing agent in place ofhydrogen or carbon monoxide. Zinc oxide bevolatile may be readilyeliminated from c reducing zone as formled. By removing instantaneouslyor at a highly intense rate the end-products of the reaction, thecounter-reaction has a value which may be made infinitely small. Thus bypass ing the stream of reducing agent at the highest practicable-ratethe reduction of a most tted subjected. Various chan 'of the elements,

tin is obtained carrying not ation of. the ,elec-f diflicultly reduciblemetal may be carried on by a rery weak reducing agent.

I have perfected, as above indicated, a method of reducing and refiningwhich is partlcularlyapphcable to ores containing elements ordinarily Aswill be understoo from the foregoing description, I am thus enabled torecover metals from such ores with facility heretofore impossible,because of the complex 0 erations to which the ores were necessari y mabe made in the details of the meth and c character and proportions ofthe materials employed without departing from the invention orsacinfi'cing any of its material advantages.

1. A method of reducing ores containing a of difiicultly separableelements, w ch comprises, subjecting the ore to a 'rehminary reduction,regulating the withawal of the gaseous tion to permit a selectivereduction of one and subsequently heating the mass in the presence ofslag forming material to scori the unreduced element.

2. A metho of reducing ores containing tin and iron, which comprises,subjecting the ore to a preliminary reduction, regulating the withdrawal'of the gaseous product of the reaction to permit selective reduction ofthe tin and su uently heating the mass in the presence of s ag formingmaterial to scori the iron.

3. method of reducing ores containing a plurality of diflicultlyseparable elements, which comprises, subjecting the' ore to a reliminaryreduction, with a gaseous r ucing medium, re lating the withdrawal ofthe gaseous pro not of the reaction to permit selective reduction of oneof the elements, and subsequently heating the mass with $13 formingmaterial to scorify the unredu element.

'4. A method of reducing ores containing tin and iron, which comprises,subjecting the ores to a reliminary reduction with a gaseous reducmgmedium, regulating the withdrawal of the gaseous product of the reactionto permit selective reduction of the tin and subsequently heating themass product of the reacwith slag forming material to scorify the 5. Amethod of reducing ores containing tin and iron, which comprises, mixingthe ore with slag forming material, reducing the tin under conditionspreventing reduction of the iron therein and subsequently heating themass to scorify and separate the iron from the tin.

6. A method of reducing ores containing iron and tin, which comprises,mixing the are with slag forming material, subjecting the mass to theaction of a gaseous reducing medium, effecting the withdrawal of gaseousy 1n the mass and heating the through medium i I regulating the reactlonto prevent reduction giermit intensive reeatingth due a nt do over,around and mg iii; comp reduced and remov ng at a end-products ction andregenerating said used reducing agent by removing the end-productsearned there 8. A method of reducing ores containing iron and tin, whichcomprises, mixing the ore with slag forming material, subjecting themass to the action of a gaseous reducing medium, regulating theconditions of the reduction to prevent reduction ofiron mass to scorifyand separate the iron from the tin.

9. A method of reducing ores contain iron and tin, which comprises,snhgecting the ore at a tempo ture from 600- 50 to the action of a. andsubsequentl eating the-mass to a. temperature rfslsnh itantially (56 int2;

resence o a orming'ma u soon 5nd so arate oi, iron from the tin. V 10.method of reducing ores containing tin and iron, which comprises,subjecting the ore to e redu action of a gaseous which hy g'enpredominates, of the iron and subsequently heating the mass in thepresence of slag forming material to separate the iron from the 11. Amethod 'of reducing. ores containing tin and iron, which, comprises,subjecting a mixture of the ore and f0 material to the action of agaseous re ucing I tight-e15 accelerated rate the one reducing medium,

reduction of iron and submuently heating the mass to a temperatureappropriate to the scorification and se aration of the iron.

12.. The process of c oridiz' 300 C. comglex tin ores so as to removeelements who form,- volatile chlorides and caching out elements which'chlorides, so as to from complex tin 0res.- 13. A method of treatingcomplex tin ores to recover tin therefrom, which comprises, ehloridi'zing the are thereby convertmgthe 1m urities into c orides,separating the ch orides, heating the ore with a gaseous reducing agent,re lating the reaction to sel ctively reduce e tin and separating thetin.

14. A method of ores contain recover tin t erefioni, which comprises,chloridizing the ore, thereby convert' g the imlp rities into chlorides,separating the ch orides, heating the orew'it ,a

ducmg agent to reduce treating complex tin iron and other impurities toacorify'the iron. 15. A method of treating vcomplex ores containing ironand other im urities to recover tin therefrom, which comprises,chloridizing the 0 thereby converting the impurities into ch orides,separating the chlorides,- heating the ore with a seous ucing agent, relating the reaction to v reducethe tin wit out reducing the iron, andsmelting the ore with slag forming material to soorify the iron.

In testimon whereof I aflix m s" ature. WO6LSEY MoA JOilfiONw mg ataround

